This is a 371 application of PCT/GB99/03636 and claims benefit from British Application No. 9824897.4, filed Nov. 12, 1998.
The present invention relates to a class of substituted pentaaza-cyclopenta[a]naphthalene derivatives and to their use in therapy. More particularly, this invention is concerned with substituted 1,2,3a,4,x-pentaaza-cyclopenta[a]naphthalene derivatives which are ligands for GABAA receptors containing the xcex15 subunit and are therefore useful in the therapy where cognition enhancement is required.
Receptors for the major inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), are divided into two main classes: (1) GABAA receptors, which are members of the ligand-gated ion channel superfamily; and (2) GABAB receptors, which may be members of the G-protein linked receptor superfamily. Since the first cDNAs encoding individual GABAA receptor subunits were cloned the number of known members of the mammalian family has grown to thirteen (six xcex1 subunits, three xcex2 subunits, three xcex3 subunits and one xcex4 subunit). It may be that further subunits remain to be discovered; however, none has been reported since 1993.
Although knowledge of the diversity of the GABAA receptor gene family represents a huge step forward in our understanding of this ligand-gated ion channel, insight into the extent of subtype diversity is still at an early stage. It has been indicated that an a subunit, a xcex2 subunit and a xcex3 subunit constitute the minimum requirement for forming a fully functional GABAA receptor expressed by transiently transfecting cDNAs into cells. As indicated above, a xcex4 subunit also exists, but is apparently uncommon in the native receptor.
Studies of receptor size and visualisation by electron microscopy conclude that, like other members of the ligand-gated ion channel family, the native GABAA receptor exists in pentameric form. The selection of at least one xcex1, one xcex2 and one xcex3 subunit from a repertoire of thirteen allows for the possible existence of more than 10,000 pentameric subunit combinations. Moreover, this calculation overlooks the additional permutations that would be possible if the arrangement of subunits around the ion channel had no constraints (i.e. there could be 120 possible variants for a receptor composed of five different subunits).
Receptor subtype assemblies which do exist include xcex11xcex22xcex32, xcex12xcex22/3xcex32, xcex13xcex2xcex32/3, xcex12xcex2xcex31, xcex15xcex23xcex32/3, xcex16xcex2xcex32, xcex16xcex2xcex4 and xcex14xcex2xcex4. Subtype assemblies containing an xcex11 subunit are present in most areas of the brain and account for over 40% of GABAA receptors in the rat. Subtype assemblies containing xcex12 and xcex13 subunits respectively account for about 25% and 17% of GABAA receptors in the rat. Subtype assemblies containing an xcex15 subunit are primarily hippocampal and represent about 4% of receptors in the rat.
A characteristic property of some GABAA receptors is the presence of a number of modulatory sites, of which the most explored is the benzodiazepine (BZ) binding site through which anxiolytic drugs such as diazepam and temazepam exert their effect. Before the cloning of the GABAA receptor gene family, the benzodiazepine binding site was historically subdivided into two subtypes, BZ1 and BZ2, on the basis of radioligand binding studies. The BZ1 subtype has been shown to be pharmacologically equivalent to a GABAA receptor comprising the xcex11 subunit in combination with xcex22 and xcex32. This is the most abundant GABAA receptor subtype, representing almost half of all GABAA receptors in the brain.
A number of dementing illnesses such as Alzheimer""s disease are characterised by a progressive deterioration in cognition in the sufferer. It would clearly be desirable to enhance cognition in subjects desirous of such treatment, for example for subjects suffering from a dementing illness.
It has been reported by McNamara and Skelton in Psychobiology, 21:101-108, that the benzodiazepine receptor inverse agonist xcex3-CCM enhanced spatial learning in the Morris watermaze. However, xcex3-CCM and other conventional benzodiazepine receptor inverse agonists are proconvulsant or convulsant which makes it clear that they cannot be used as cognition enhancing agents in humans.
However, we have now discovered that it is possible to obtain medicaments which have cognition enhancing effects which may be employed with less risk of proconvulsant effects previously described with benzodiazepine receptor partial or full inverse agonists.
It has now been discovered that use of an xcex15 receptor partial or full inverse agonist which is relatively free of activity at xcex11 and/or xcex12 and/or xcex13 receptor binding sites can be used to provide a medicament which is useful for enhancing cognition but in which proconvulsant activity is reduced or eliminated. Inverse agonists at xcex15 which are not free of activity at xcex11 and/or xcex12 and/or xcex13 but which are functionally selective for xcex15 can also be used. Inverse agonists which are both selective for xcex15 and are relatively free of activity at xcex11, xcex12 and xcex13 receptor binding sites are preferred.
European Patent Applications 0085840 and 0134946 describe related series of 1,2,4-triazolo[3,4-a]phthalazine derivatives which are stated to possess antianxiety activity. However, there is no disclosure nor any suggestion in either of these publications of the compounds of the present invention, nor that the compounds disclosed in the Applications have any cognition enhancing properties.
The present invention provides a compound of the formula I: 
wherein:
R1 is hydrogen, halogen or CN or a group CF3, OCF3, C1-4alkyl, C2-4alkenyl, C2-4alkynyl, C1-4alkoxy, C2-4alkenyloxy or C2-4alkynyloxy, each of which groups is unsubstituted or substituted with one or two halogen atoms or with a pyridyl or phenyl ring each of which rings may be unsubstituted or independently substituted by one or two halogen atoms or nitro, cyano, amino, methyl or CF3 groups;
R2 is hydrogen, halogen or CN or a group CF3, OCF3, C1-4alkyl, C2-4alkenyl, C2-4alkynyl, C1-4alkoxy, C2-4alkenyloxy or C2-4alkynyloxy each of which groups is unsubstituted or substituted with one or two halogen atoms;
L is O, S or NRn where Rn is H, C1-6alkyl or C3-6cycloalkyl;
one of T1, T2, T3 and T4 is nitrogen or N+xe2x80x94Oxe2x88x92 and the others are CH;
X is a 5-membered heteroaromatic ring containing 1, 2, 3 or 4 heteroatoms independently chosen from oxygen, nitrogen and sulphur, at most one of the heteroatoms being oxygen or sulphur, or a 6-membered heteroaromatic ring containing 1, 2 or 3 nitrogen atoms, the 5- or 6-membered heteroaromatic ring being optionally fused to a benzene ring and the heteroaromatic ring being optionally substituted by Rx and/or Ry and/or Rz, where Rx is halogen, R3, OR3, OCOR3, NR4R5, NR4COR5, tri(C1-6alkyl)silylC1-6alkoxyC1-4alkyl, CN or R9, Ry is halogen, R3, OR3, OCOR3, NR4R5, NR4COR5 or CN and Rz is R3, OR3 or OCOR3, where R3 is C1-6alkyl, C2-6alkenyl, C2-6alkynyl, C3-6cycloalkyl, hydroxyC1-6alkyl and R3 is optionally mono, di- or tri-fluorinated, R4 and R5 are each independently hydrogen, C1-6alkyl, C2-6alkenyl, C2-6alkynyl, C3-6cycloalkyl or CF3 or R4 and R5, together with the nitrogen atom to which they are attached, form a 4-7 membered heteroaliphatic ring containing the nitrogen atom as the sole heteroatom, and R9 is benzyl or an aromatic ring containing either 6 atoms, 1, 2 or 3 of which are optionally nitrogen, or 5 atoms, 1, 2 or 3 of which are independently chosen from oxygen, nitrogen and sulphur, at most one of the atoms being oxygen or sulphur, and R9 is optionally substituted by one, two or three substituents independently chosen from halogen atoms and C1-4alkyl, C2-4alkenyl, C2-4alkynyl, C1-4alkoxy, C2-4alkenyloxy and C2-4alkynyloxy groups each of which groups is unsubstituted or substituted by one, two or three halogen atoms, and when X is a pyridine derivative, the pyridine derivative is optionally in the form of the N-oxide and providing that when X is a tetrazole derivative it is protected by a C1-4alkyl group; or X is phenyl optionally substituted by one, two or three groups independently selected from halogen, cyano, C1-6alkyl, C2-6alkenyl, C2-6alkynyl and C3-6cycloalkyl;
Y is optionally branched C2-4alkylene or C1-4alkylidene optionally substituted by an oxo group or Y is a group (CH2)jO wherein the oxygen atom is nearest the group X and j is 2, 3 or 4;
Z is a 5-membered heteroaromatic ring containing 1, 2 or 3 heteroatoms independently selected from oxygen, nitrogen and sulphur, at most one of the heteroatoms being oxygen or sulphur and providing that when one of the atoms is oxygen or sulphur then at least one nitrogen atom is present, or a 6-membered heteroaromatic ring containing 2 or 3 nitrogen atoms, Z being optionally substituted by Rv and/or Rw, where Rv is halogen, R6, NR7R8, NR7COR8, CN, furyl, thienyl, phenyl, benzyl, pyridyl or a 5-membered heteroaromatic ring containing at least one nitrogen atom and optionally 1, 2 or 3 other heteroatoms independently selected from oxygen, nitrogen and sulphur, at most one of the other heteroatoms being oxygen or sulphur and Rw is R6 or CN;
R6 is C1-6alkyl, C2-6alkenyl, C2-6alkynyl, C3-6cycloalkyl, hydroxyC1-6alkyl, C1-6alkoxy, C2-6alkenyloxy, C2-6alkynyloxy, C1-6alkoxyC1-6alkyl, CH2F or CF3; and
R7 and R8 are each independently hydrogen, C1-6alkyl, C2-6alkenyl, C2-6alkynyl, C3-6cycloalkyl or CF3 or R7 and R8, together with the nitrogen atom to which they are attached, form a 4-7 membered heteroaliphatic ring containing the nitrogen atom as the sole heteroatom;
or a pharmaceutically acceptable salt thereof.
In a particular embodiment of the invention, one of T1, T2, T3 and T4 is nitrogen and the others are CH, and Y is optionally branched C1-4alkylidene optionally substituted by an oxo group or Y is a group (CH2)jO wherein the oxygen atom is nearest the group X and j is 2, 3 or 4.
The compound is generally in the form of the free base.
As used herein, the expression xe2x80x9cC1-6alkylxe2x80x9d includes methyl and ethyl groups, and straight-chained and branched propyl, butyl, pentyl and hexyl groups. Particular alkyl groups are methyl, ethyl, n-propyl, isopropyl and t-butyl. Derived expressions such as xe2x80x9cC1-4alkylxe2x80x9d, xe2x80x9cC2-4alkenylxe2x80x9d, xe2x80x9cC2-6alkenylxe2x80x9d, xe2x80x9chydroxyC1-6alkylxe2x80x9d, xe2x80x9cC2-4alkylxe2x80x9d and xe2x80x9cC2-6alkynylxe2x80x9d are to be construed in an analogous manner.
As used herein, the expression xe2x80x9cC1-4alkylidenexe2x80x9d refers to alkanediyl groups having the free valancies on the same carbon atom, while the expression. xe2x80x9cC2-4alkylenexe2x80x9d refers to alkanediyl groups having the free valencies on different carbon atoms.
The expression xe2x80x9cC3-6cycloalkylxe2x80x9d as used herein includes cyclic propyl, butyl, pentyl and hexyl groups such as cyclopropyl and cyclohexyl.
Suitable 5- and 6-membered heteroaromatic rings include pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, pyrrolyl, pyrazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, oxadiazolyl and thiadiazolyl groups. A suitable 5-membered heteroaromatic ring containing four nitrogen atoms is tetrazolyl. Suitable 6-membered heteroaromatic rings containing three nitrogen atoms include 1,2,4-triazine and 1,3,5-triazine.
The term xe2x80x9chalogenxe2x80x9d as used herein includes fluorine, chlorine, bromine and iodine, of which fluorine and chlorine are preferred.
As used herein the term xe2x80x9cC1-6alkoxyxe2x80x9d includes methoxy and ethoxy groups, and straight-chained, branched and cyclic propoxy, butoxy, pentoxy and hexoxy groups, including cyclopropylmethoxy. Derived expressions such as xe2x80x9cC2-6alkenyloxyxe2x80x9d, xe2x80x9cC2-6alkynyloxyxe2x80x9d, xe2x80x9cC1-4alkoxyxe2x80x9d, xe2x80x9cC2-4alkenyloxyxe2x80x9d and xe2x80x9cC2-4alkyloxyxe2x80x9d should be construed in an analogous manner.
R1 may be hydrogen, halogen or CN or a group C1-4alkyl, C2-4alkenyl, C2-4alkynyl, C1-4alkoxy, C2-4alkenyloxy or C2-4alkynyloxy, each of which groups is unsubstituted or substituted with one or two halogen atoms or with a pyridyl or phenyl ring each of which rings may be unsubstitutecd or independently substituted by one or two halogen atoms or nitro, cyano, amino, methyl or CF3 groups. R1 is typically hydrogen, fluorine, chlorine, bromine or a group C1-4alkyl, C2-4alkenyl, C2-4alkynyl, C1-4alkoxy, C2-4alkenyloxy or C2-4alkynyloxy, each of which groups is unsubstituted or substituted with one or two halogen atoms or by a pyridyl or phenyl ring each of which rings may be unsubstituted or substituted by one or two halogen atoms or nitro, cyano, amino, methyl or CF3 groups and is generally hydrogen, fluorine or pyridylmethoxy, typically hydrogen.
R2 may be hydrogen, halogen or CN or a group C1-4alkyl, C2-4alkenyl, C2-4alkynyl, C1-4alkoxy, C2-4alkenyloxy or C2-4alkynyloxy each of which groups is unsubstituted or substituted with one or two halogen atoms. R2 is typically hydrogen, fluorine, chlorine or bromine, and is generally hydrogen or fluorine, typically hydrogen.
Preferably L is an oxygen atom. L may also be NRn in which Rn is preferably hydrogen or methyl. Rn may be hydrogen.
X is generally: pyridyl, pyrazinyl, pyridazinyl or pyrimidinyl optionally substituted by a halogen atom or a group and X is optionally fused to a benzene ring; a 5-membered heteroaromatic ring containing 2 or 3 heteroatoms chosen from oxygen, sulphur and nitrogen, at most one of the heteroatoms being oxygen or sulphur, which is unsubstituted or substituted by one, two or three groups independently chosen from halogen and R3, or which is substituted by a pyridyl, phenyl or benzyl ring which ring is optionally independently substituted by one, two or three halogen atoms or C1-6alkyl or CF3 groups; or phenyl optionally substituted by one, two or three independently chosen halogen atoms. In particular X is pyridyl, pyrazinyl, pyridazinyl or pyrimidinyl which is unsubstituted or substituted by methyl, CF3, methoxy, bromine, chlorine, isopropoxy, dimethylamino or a 5-membered heterocyclic ring containing 1, 2 or 3 nitrogen atoms, and X is optionally fused to a benzene ring, or X is pyrazolyl, isothiazolyl, isoxazolyl, 1,2,4-triazolyl, thiazolyl, 1,2,3-triazolyl or imidazolyl which is unsubstituted or substituted by one, two or three groups independently chosen from methyl, CF3 and chlorine or is substituted by a phenyl, benzyl or pyridyl ring which ring is unsubstituted or substituted by chlorine or CF3, or X is phenyl which is unsubstituted or substituted by chlorine. Specific values of X are 2-pyridyl, 6-methylpyridin-2-yl, 3-pyridyl, 4-pyridyl, 3,5-dimethylpyrazol-1-yl, 3-methoxypyridin-2-yl, 3-methylisoxazol-5-yl, pyrazol-1-yl, 6-chloropyridin-2-yl, 6-bromopyridin-2-yl, 6-methoxypyridin-2-yl, 6-isopropoxypyridin-2-yl, 6-N,N-dimethylpyridin-2-yl, 6-(imidazol-1-yl)pyridin-2-yl, 3-pyridazino, 4-pyrimidinyl, pyrazin-2-yl, 2-quinolinyl, 2-quinoxalyl, 2-(4-trifluoromethyl)pyridyloxy, 4-methylisothiazolyl, 2,6-dichlorophenyl, 4-methylthiazol-5-yl, 2-methylthiazol-4-yl, 2-[1-(3-trifluoromethyl)pyrid-6-yl]imidazolyl, 1-benzylimidazol-2-yl, 1-(4-chlorophenyl)-1,2,3-triazol-4-yl, 3-chloro-2-methyl-5-trifluoromethylpyrazol-4-yl, 1-methyl-1,2,4-triazol-3-yl, (5-trifluoromethyl)pyridyl-2-yl, (3-trifluoromethyl)pyrid-2-yl, (4-trifluoromethyl)pyrid-2-yl, 1-methylimidazol-2-yl, 2-{[2-(trimethylsilyl)ethoxy]methyl}-1,2,4-triazol-3-yl, 3-methylimidazol-4-yl, 1,2,4-triazol-3-yl, 1-isopropyl-1,2,4-triazol-3-yl, 4-methyl-1,2,4-triazol-3-yl, 1,2,3-triazol-4-yl, isothiazol-3-yl, 1-ethyl-1,2,4-triazol-3-yl, 2-methyl-1,2,3-triazol-4-yl, 1-methyl-1,2,3-triazol-4-yl, 2-methyl-1, 2,4-triazol-3-yl, 1-methylimidazol-4-yl, 5-tert-butylpyridazin-3-yl and 1-methyl-1,2,3-triazol-5-yl. Still further particular values of X are 2-benzyl-1,2,4-triazol-3-yl, 1-benzyl-1,2,4-triazol-3-yl, 1-nbutyl-1,2,4-triazol-3-yl, 2-ethyl-1,2,4-triazol-3-yl, 2-methylpyrazol-3-yl, 1-methylpyrazol-3-yl, 1-npropyl-1,2,4-triazol-3-yl, 1-(2,2,2-trifluorethyl)-1,2,4-triazol-3-yl, 1-ethyl-1,2,3-triazol-5-yl, 1-methyltetrazol-2-yl, imidazol-2-yl, 2-npropyl-1,2,4-triazol-3-yl, 1-ethyl-1,2,3-triazol-4-yl, 2-ethyl-1,2,3-triazol-4-yl, 1-ethylimidazol-5-yl, 1-ethylimidazol-4-yl, 1-npropyl-1,2,4-triazol-3-yl and 1-ethyl-1,2,3-triazol-5-yl. In particular X is pyrid-2-yl, 2-methyl-1,2,4-triazol-3-yl, 1-methyl-1,2,4-triazol-3-yl, 1-methyl-1,2,3-triazol-4-yl, 3-methyl-1,2,3-triazol-4-yl or 2-ethyl-1,2,4-triazol-3-yl.
When X is a substituted 6-membered heteroaromatic ring: Rx is preferably halogen, R3, OR3, NR4R5 or a five-membered heteroaromatic ring containing 1, 2 or 3 nitrogen atoms and more preferably methyl, CF3, methoxy, bromine, chlorine, isopropoxy, dimethylamino or a five-membered heterocyclic ring containing 1, 2 or 3 nitrogen atoms; and Ry and Rz are preferably absent. In particular X is optionally substituted pyridine. The optional substituents are generally CF3, halogen or C1-6alkyl, particularly methyl or ethyl, especially methyl. When X is pyridine it may be in the form of the N-oxide.
When X is a substituted 5-membered heteroaromatic ring: Rx is preferably halogen, R3 or a pyridyl, phenyl or benzyl ring which ring is optionally independently substituted by one, two or three halogen atoms or C1-6alkyl or CF3 groups and more preferably Rx is methyl, CF3, chlorine or a phenyl, pyridyl or benzyl ring which ring is unsubstituted or substituted by chlorine or CF3; and Ry and Rz are preferably halogen or R3, and more preferably methyl, CF3 or chlorine. X is especially an optionally substituted triazole, either a 1,2,3- or 1,2,4-triazole, which is preferably substituted by methyl or ethyl, especially methyl.
Particularly aptly X is an unsubstituted six-membered heteroaromatic group containing one or two nitrogen atoms.
Apt values for Y include CH2, CH(CH3), CH2CH2 and CH2CH2CH2 optionally substituted by an oxo group, and CH2CH2O and CH2CH2CH2O. For example, Y can be CH2, CH2CH2, CH2CH2CH2, CH2CH2O or CH2CH2CH2O. Preferably Y is CH2 or CH2CH2 and most preferably CH2.
Rv is suitably chlorine, R6, thienyl, furyl, pyridyl or NR7R8, more particularly R6, thienyl, furyl, pyridyl or NR7R8, for example C1-6alkyl, C3-6cycloalkyl, hydroxyC1-6alkyl, pyridyl, thienyl or amino and more particularly methyl, ethyl, ethoxy, isopropyl, cyclopropyl, thienyl or pyridyl, and even more particularly methyl, ethyl, isopropyl, cyclopropyl, thienyl or pyridyl. A further example of Rv is chlorine.
Rw is suitably R6, for example C1-6alkyl, CH2F or hydroxyC1-6alkyl, more particularly methyl, CH2F or hydroxymethyl. Generally Rw is absent.
Rx may be halogen, R3, OR3, OCOR3, NR4R5, NR4COR5, CN or R9.
Z is preferably a 5-membered heteroaromatic ring containing 1, 2 or 3 heteroatoms independently selected from oxygen, nitrogen and sulphur, at most one of the heteroatoms being oxygen or sulphur and providing that when two of the heteroatoms are nitrogen an oxygen or sulphur atom is also present and that when one of the atoms is oxygen or sulphur then at least one nitrogen atom is present, or a 6-membered heteroaromatic ring containing 2 or 3 nitrogen atoms, Z being optionally substituted by Rv and/or Rw, where Rv is halogen, R6, NR7R8, NR7COR8, CN, furyl, thienyl, phenyl, benzyl, pyridyl or a 5-membered heteroaromatic ring containing at least one nitrogen atom and optionally 1, 2 or 3 other heteroatoms independently selected from oxygen, nitrogen and sulphur, at most one of the other heteroatoms being oxygen or sulphur and Rw, is R6 or CN.
Suitable values for Z include pyrimidinyl, pyrazinyl, pyrrolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, oxadiazolyl and thiadiazolyl groups which groups are optionally substituted by R6, thienyl, furyl, pyridyl or NR7R8 groups.
Z is very aptly a 5-membered heteroaromatic ring containing one oxygen and one or two nitrogen ring atoms and is optionally substituted by, a group R6. In such compounds R3 is favourably a methyl group.
Favoured values for Z include optionally substituted isoxazoles and oxadiazoles.
Z may be unsubstituted.
Z may very aptly be substituted by methyl.
Z is especially isoxazole which is unsubstituted or substituted by C1-6alkyl or C1-6alkoxy, especially methyl or ethoxy.
Particular values of Z are 3-methyloxadiazol-5-yl, 3-cyclopropyloxadiazol-5-yl, 5-methylisoxazol-3-yl, 5-(3-pyridyl)-isoxazol-3-yl, 5-hydroxymethylisoxazol-3-yl, 4,5-dimethylisoxazol-3-yl, 5-ethylisoxazol-3-yl, 5-cyclopropylisoxazol-3-yl, 5-isopropylisoxazol-3-yl, isoxazol-3-yl, 5-thienylisoxazol-3-yl, 5-fluoromethylisoxazol-3-yl, 4-methylisoxazol-3-yl, 5-ethoxylsoxazol-3-yl, 4-methyl-5-chloroisoxazol-3-yl, 5-trifluoromethylisoxazol-3-yl, 5-(pyrid-2-yl)isoxazol-3-yl, 5-benzylisoxazol-3-yl, 5-chloroisoxazol-3-yl, 3-cyclopropyloxadiazol-5-yl, 5-methoxylsoxazol-3-yl, 5-methoxymethylisoxazol-3-yl, 5-methyloxadiazol-3-yl, pyrazin-2-yl and 3-methylisoxazol-5-yl. In particular Z is 5-methylisoxazol-3-yl, isoxazol-3-yl or 5-ethoxylsoxazol-3-yl.
R3 may be C1-6alkyl, C2-6alkenyl, C2-6alkynyl, C3-6cycloalkyl, hydroxyC1-6alkyl or CF3.
Generally R3 is C1-6alkyl, C2-6alkoxy or CF3. In particular R3 is methyl, methoxy, ispropoxy or trifluoromethyl.
Generally R4 and R5 are independently hydrogen or C1-6alkyl, in particular hydrogen or methyl, for example both can be methyl.
R6 may be C1-6alkyl, C2-6alkenyl, C2-6alkynyl, C3-6Cycloalkyl, hydroxyC1-6alkyl, C1-6alkoxy, C2-6alkenyloxy, C2-6alkynyloxy, CH2F or CF3. Generally R6 is CH2F, CF3, C1-6alkoxy, C3-6cycloalkoxy, C1-6alkyl or hydroxyC1-6alkyl, for example, CH2F, CF3, methyl, ethyl, iospropyl, cyclopropyl or hydroxymethyl, particularly methyl or cyclopropyl. Alternatively R6 is C1-6alkyl or hydroxyC1-6alkyl, for example, methyl, ethyl, isipropyl, cyclopropyl or hydroxymethyl.
Generally R7 and R8 are independently hydrogen or C1-6alkyl, particularly hydrogen or methyl.
Generally R9 is pyrazolyl, imidazolyl, phenyl, benzyl or pyridyl optionally substituted by halogen, preferably chlorine, or CF3. In particular R9 can be imidazol-1-yl, 3-trifluoromethylpyrid-5-yl, benzyl and 4-chlorophenyl.
Generally R10 is C1-6alkyl or CF3, in particular methyl or CF3, for example CF3.
One of T1, T2, T3 and T4 represents N or N+xe2x80x94Oxe2x80x94 while the others represent CH. Thus, the compounds of the invention are 1,2,3a,4,x-pentaaza-cyclopenta[a]naphthalene derivatives, where x is 6, 7, 8 or 9, or the corresponding 6-, 7-, 8-, or 9-N-oxides. Preferably, one of T1, T2, T3 and T4 represents N, most preferably T3 or T4 represents N.
In a preferred subclass of compounds of formula I:
R1 and R2 are hydrogen;
L is O;
X is pyridine or triazole and is unsubstituted or substituted by C1-6alkyl or CF3;
Y is CH2; and
Z is isoxazole which is unsubstituted or substituted by C1-6alkyl or C1-6alkoxy.
In a particular embodiment of this subclass, X is pyridine or triazole and is unsubstituted or substituted by C1-6alkyl.
For use in medicine, the salts of the compounds of formula I will be pharmaceutically acceptable salts. Hence in a favoured aspect this invention provides the compounds of the formula I and pharmaceutically acceptable salts thereof. Other salts may, however, be useful in the preparation of the compounds according to the invention or of their pharmaceutically acceptable salts. Suitable pharmaceutically acceptable salts of the compounds of this invention include acid addition salts which may, for example, be formed by mixing a solution of the compound according to the invention with a solution of a pharmaceutically acceptable acid such as hydrochloric acid, sulphuric acid, methanesulphonic acid, fumaric acid, maleic acid, succinic acid, acetic acid, benzoic acid, oxalic acid, citric acid, tartaric acid or phosphoric acid. Furthermore, where the compounds of the invention carry an acidic moiety, suitable pharmaceutically acceptable salts thereof may include alkali metal salts, e.g. sodium or potassium salts; alkaline earth metal salts, e.g. calcium or magnesium salts; and salts formed with suitable organic ligands, e.g. quaternary ammonium salts.
Where the compounds according to the invention have at least one asymmetric centre, they may accordingly exist as enantiomers. Where the compounds according to the invention possess two or more asymmetric centres, they may additionally exist as diastereoisomers. It is to be understood that all such isomers and mixtures thereof in any proportion are encompassed within the present invention.
It will be understood by the skilled person that when a five-membered heterocyclic ring is referred to in the foregoing having four heteroatoms in the ring, then all these heteroatoms are nitrogen. It will further be understood that when a substituted five-membered heterocyclic ring is referred to having two nitrogen atoms and an oxygen or sulphur atom in the ring, then only one substituent may be present so that aromaticity is maintained. Thus, for example, in such a case X may only be substituted by Rx and Z may only be substituted by Rv.
Specific compounds within the scope of the present invention include:
3-(5-methylisoxazol-3-yl)-5-(2-pyridylmethyloxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(2-pyridylmethyloxy)-1,2,3a,4,9-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(2-pyridylmethyloxy)-1,2,3a,4,7-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(2-pyridylmethyloxy)-1,2,3a,4,8-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(2-methyl-1,2,4-triazol-3-ylmethyloxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-ethoxylsoxazol-3-yl)-5-(1-methyl-1,2,4-triazol-3-ylmethyloxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-isoxazol-3-yl-5-(2-methyl-1,2,4-triazol-3-ylmethoxy)-1,2,3a,4,6-pentaatza-cyclopenta[a]naphthalene;
3-isoxazol-3-yl-5-(1-methyl-1,2,4-triazol-3-ylmethoxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(1-methyl-1,2,4-triazol-3-ylmethoxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(1-methyl-1,2,3-triazol-4-ylmethoxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(3-methyl-1,2,3-triazol-4-ylmethoxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(2-ethyl-1,2,4-triazol-3-ylmethoxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-ethoxylsoxazol-3-yl)-5-(1-methyl-1,2,3-triazol-4-ylmethoxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-ethoxylsoxazol-3-yl)-5-(3-methyl-1,2,3-triazol-4-ylmethoxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
3-(5-ethoxylsoxazol-3-yl)-5-(2-ethyl-1,2,4-triazol-3-ylmethoxy)-1,2,3a,4,6-pentaaza-cyclopenta[a]naphthalene;
and pharmaceutically acceptable salts thereof.
Further specific compounds within the scope of the invention include:
3-(5-methylisoxazol-3-yl)-5-(2-pyridylmethyloxy)-1,2,3a,4,7-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(1-methyl-1,2,3-triazol-4-ylmethyloxy)-1,2,3a,4,7-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(1-methyl-1,2,4-triazol-3-ylmethyloxy)-1,2,3a,4,7-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(3-trifluoromethyl-2-pyridylmethyloxy)-1,2,3a,4,7-pentaaza-cyclopenta[a]naphthalene;
3-(5-methylisoxazol-3-yl)-5-(1-methyl-1,2,3-triazol-4-ylmethyloxy)-7-oxide-1,2,3a,4,7-pentaaza-cyclopenta[a]naphthalene;
and pharmaceutically acceptable salts thereof.
Examples of pharmaceutically acceptable salts are hydrochlorides, sulfates, citrates, tartrates, acetates, methanesulfonates, phosphates, oxalates and benzoates.
The compounds of the present invention have a good binding affinity (Ki) for the xcex15 subunit. In a preferred embodiment the compounds of the invention are binding selective for the xcex15 subunit relative to the xcex11, 2 and xcex13 subunits. In another preferred embodiment the compounds are functionally selective for the xcex15 subunit as partial or full inverse agonists whilst substantially being antagonists at the xcex11, xcex12 and xcex13 subunits.
Cognition enhancement can be shown by testing the compounds in the Morris watermaze as reported by McNamara and Skelton, Psychobiology, 21:101-108. The functional efficacy at the various receptor subtypes can be calculated using the method disclosed in WO-A-9625948.
The invention also provides pharmaceutical compositions comprising one or more compounds of this invention and a pharmaceutically acceptable carrier. Preferably these compositions are in unit dosage forms such as tablets, pills, capsules, powders, granules, sterile parenteral solutions or suspensions, metered aerosol or liquid sprays, drops, ampoules, transdermal patches, auto-injector devices or suppositories; for oral, parenteral, intranasal, sublingual or rectal administration, or for administration by inhalation or insufflation. For preparing solid compositions such as tablets, the principal active ingredient is mixed with a pharmaceutical carrier, e.g. conventional tableting ingredients such as corn starch, lactose, sucrose, sorbitol, talc, stearic acid, magnesium stearate, dicalcium phosphate or gums or surfactants such as sorbitan monooleate, polyethylene glycol, and other pharmaceutical diluents, e.g. water, to form a solid preformulation composition containing a homogeneous mixture of a compound of the present invention, or a pharmaceutically acceptable salt thereof. When referring to these preformulation compositions as homogeneous, it is meant that the active ingredient is dispersed evenly throughout the composition so that the composition may be readily subdivided into equally effective unit dosage forms such as tablets, pills and capsules. This solid preformulation composition is then subdivided into unit dosage forms of the type described above containing from 0.1 to about 500 mg of the active ingredient of the present invention. Typical unit dosage forms contain from 1 to 100 mg, for example 1, 2, 5, 10, 25, 50 or 100 mg, of the active ingredient. The tablets or pills of the novel composition can be coated or otherwise compounded to provide a dosage form affording the advantage of prolonged action. For example, the tablet or pill can comprise an inner dosage and an outer dosage component, the latter being in the form of an envelope over the former. The two components can be separated by an enteric layer which serves to resist disintegration in the stomach and permits the inner component to pass intact into the duodenum or to be delayed in release. A variety of materials can be used for such enteric layers or coatings, such materials including a number of polymeric acids and mixtures of polymeric acids with such materials as shellac, cetyl alcohol and cellulose acetate.
The present invention also provides a compound of the invention for use in a method of treatment of the human body. Preferably the treatment is for a condition associated with GABAA receptors comprising the xcex15 subunit and/or for the enhancement of cognition. Preferably the condition is a neurological deficit with an associated cognitive disorder such as a dementing illness such as Alzheimer""s disease. Other conditions to be treated include cognition deficits due to traumatic injury, stroke, Parkinson""s disease, Downs syndrome, age related memory deficits, attention deficit disorder and the like.
Thus, for example, the compounds of the present invention can be used in a variety of disorders of the central nervous system. Such disorders include delirium, dementia and amnestic and other cognitive disorders. Examples of delirium are delirium due to substance intoxication or substance withdrawal, delirium due to multiple etiologies and delirium NOS (not otherwise specified). Examples of dementia are: dementia of the Alzheimer""s type with early onset which can be uncomplicated or with delirium, delusions or depressed mood; dementia of the Alzheimer""s type, with late onset, which can be uncomplicated or with delirium, delusions or depressed mood; vascular dementia which can be uncomplicated or with delirium, delusions or depressed mood; dementia due to HIV disease; dementia due to head trauma; dementia due to Parkinson""s disease; dementia due to Huntington""s disease; dementia due to Pick""s disease; dementia due to Creutzfeld-Jakob disease; dementia which is substance-induced persisting or due to multiple etiologies; and dementia NOS. Examples of amnestic disorders are amnestic disorder due to a particular medical condition or which is substance-induced persisting or which is amnestic disorder NOS.
Those compounds which are not inverse agonists at the xcex15 subtype may be used as alcohol antagonists or to treat obesity.
The present invention further provides the use of a compound of the present invention in the manufacture of a medicament for the enhancement of cognition, preferably in a human suffering from a dementing illness such as Alzheimer""s disease.
Also disclosed.is a method of treatment of a subject suffering from a cognition deficit, such as that resulting from a dementing illness such as Alzheimer""s disease, which comprises administering to that subject an effective amount of a compound according to the present invention.
The liquid forms in which the novel compositions of the present invention may be incorporated for administration orally or by injection include aqueous solutions, suitably flavoured syrups, aqueous or oil suspensions, and flavoured emulsions with edible oils such as cottonseed oil, sesame oil, coconut oil or peanut oil, as well as elixirs and similar pharmaceutical vehicles. Suitable dispersing or suspending agents for aqueous suspensions include synthetic and natural gums such as tragacanth, acacia, alginate, dextran, sodium carboxymethylcellulose, methylcellulose, polyvinyl-pyrrolidone or gelatin.
For the enhancement of cognition, a suitable dosage level is about 0.01 to 250 mg/kg per day, preferably about 0.01 to 100 mg/kg per day, and especially about 0.01 to 5 mg/kg of body weight per day. The compounds may be administered on a regimen of 1 to 4 times per day. In some cases, however, dosage outside these limits may be used.
It is preferred that the compounds of the present invention are ground, for example using a pestle and mortar or industrial equivalent thereto, to a particle size of between 1 and 10 xcexcM, and preferably less than 5 xcexcM, before formulation. The compounds may be micronised or sonicised by methods known in the art or nanonised, for example by methods disclosed in U.S. Pat. No. 5,145,684.
The compounds in accordance with the present invention may be prepared by a process which comprises reacting a compound of formula III with a compound of formula IV: 
wherein T1, T2, T3, T4, R1, R2, X and Y are as defined above, G is a leaving group such as chlorine, OCH2CF3 or tosylate, B is LH where L is as defined above and Z1 is a group Z as defined above or is a moiety which can be converted into a group Z by further reaction.
Compounds of formula III represent a further feature of the present invention. The groups Z which are preferred for compounds of formula I are preferred for these compounds likewise.
The reaction between compounds III and IV when L is O is conveniently effected by stirring the reactants in a suitable solvent, typically N,N-dimethylformamide, in the presence of a strong base such as sodium hydride or lithium bis(trimethylsiiyl)amide, typically without heating and under an inert atmosphere such as nitrogen. When L is NRn, the reaction is conveniently effected in the presence of a strong base such as Et3N or NaH and a solvent such as DMF or DMSO generally for 15 to 60 hours with heating to 50-120xc2x0 C.
The intermediates of formula III above may be prepared by reacting a compound of formula V, which constitutes a further feature of the present invention, with a compound of formula VI: 
wherein T1, T2, T3, T4, R1, R2, G and Z1 are as defined above, and W represents a suitable leaving group such as C1-6alkoxy, chlorine or hydroxy.
The reaction is advantageously conducted in an inert organic solvent, generally in the presence of an organic nitrogen base and preferably under an inert atmosphere such as nitrogen. Suitable solvents include xylene, dioxane, tetrahydrofuran and lower aliphatic halogenated and aromatic hydrocarbons. Suitable organic nitrogen bases that may be employed include trialkylamines and pyridine. The reaction is generally conducted at a temperature range of from xe2x88x9220xc2x0 C. to the reflux temperature of the reaction mixture, for a period of time that depends on the reactants employed and the temperature at which the reaction is carried out. The compound of formula VI may be activated by reacting with a compound such as bis (2-oxo-3-oxazolidinyl)phosphinic chloride or 1,1xe2x80x2-dicarbonyldiimidazole before reaction with the hydrazine.
When Z1 is not a group Z, it is, for example, an allylformyloxime group which can be converted to a carboxaldehydeoxime using tetrakis(triphenylphosphine)palladium(0) generally under an inert atmosphere such as nitrogen in the presence of triethylammonium formate, in a solvent such as ethanol for about 18 hours. The carboxaldehydeoxime can be converted to a carboxaldehydechloroxime by reacting with a chlorinating agent such as N-chlorosuccinimide in a solvent such as DMP. The carboxaldehydechloroxime can be converted to the desired group Z by reacting with an unsaturated compound such a vinylidene chloride, methyl propargyl ether, 3-phenyl-1-propyne, 2-pyridylacetylene, trifluoromethylacetylene or ethoxyacetylene generally in the presence of a base such a triethylamine, and a solvent such as dichloromethane. Alternatively, the carboxaldehydechloroxime can be converted to a group Z by reacting with ammonium hydroxide generally in a solvent such as ethanol for about 30 minutes and then acetic anhydride generally with heating to reflux for about 16 hours.
Compounds of formula III in which G is OCH2CF3 can be prepared by reacting a compound of formula III in which G is chlorine with 2,2,2-trifluoroethanol in the presence of a base such as lithium bis(trimethylsilyl)amide generally in a solvent such as DMF, preferably with cooling to about xe2x88x9220xc2x0 C.-0xc2x0 C. for a period of about 30 minutes.
The compound of formula V is prepared by reaction of a compound of formula VII: 
where T1, T2, T3, T4, R1, R2 and G are as defined above, and Gxe2x80x2 is another suitable leaving group which may be the same as or different to G, with hydrazine, usually in the form of its monohydrate, generally in a solvent, such as ethanol and generally by refluxing for a suitable period such as 15 minutes to 2 hours.
As the compound of formula VII is asymmetrical, the substitution pattern about the fused benzene ring is not symmetrical. Consequently the reaction between this compound and hydrazine will usually give rise to a mixture of isomeric products depending on whether group G or Gxe2x80x2 is displaced first. Thus in addition to the required product of formula V, the isomeric compound wherein the R1 and R2 moieties are reversed or where the nitrogen atom in the fused pyridine ring is in its alternative location, will usually be obtained to some extent. For this reason it will generally be necessary to separate the resulting mixture of isomers by conventional methods such as chromatography.
The compound of formula VII can be used to prepare a compound of formula III in a single step by reacting with the appropriate hydrazoic acid, that is a compound of formula XIII:
H2NNHC(O)Zxe2x80x83xe2x80x83(XIII)
wherein Z is as defined above. This is generally carried out in the presence of a base, such as triethylamine, in a solvent such as xylene, at reflux under an inert atmosphere such as nitrogen.
The compound of formula VII can be prepared by reacting a compound of formula X: 
where T1, T2, T3, T4, R1 and R2 are as defined above, with a suitable reagent for introducing leaving groups G and G1, for example where G and G1 are both chlorine POCl3 can be used generally with heating to reflux for about 16 hours.
The compound of formula X can be prepared by reacting a compound of formula XI with hydrazine hydrate (H2NNH2.H2O): 
where T1, T2, T3, T4, R1 and R2 are as defined above. The reaction is generally carried out in a protic solvent, such as 40% aqueous acetic acid, and in the presence of a buffering agent such as sodium acetate, generally with heating to reflux for about 16 hours to about 4 days.
The compound of formula XI can be prepared by reaction of a compound of formula XII: 
wherein T1, T2, T3 and T4 are as defined above with suitable reagents to introduce the substituents R1 and R2 where necessary. For example, when R1 is phenyloxy or pyridyloxy or a derivative thereof, the corresponding hydroxy compound can be used as a reagent. The compounds of formula XII are commercially available.
Alternatively, when R1 is the same as Lxe2x80x94Yxe2x80x94X in the compound of formula I, it can be introduced by displacing another group R1 which can act as a leaving group, such as fluorine, in the reaction between the compounds of formulae III and IV.
In another procedure, the compounds according to the invention wherein L is O may be prepared by a process which comprises reacting a compound of formula VIII with a compound of formula IX: 
wherein T1, T2, T3, T4, R1, R2, X, Y and Z are as defined above and J represents a suitable leaving group such as a halogen atom, typically chlorine. The reaction between compounds VIII and IX is conveniently effected by stirring the reactants in a suitable solvent, typically N,N-dimethylformamide, in the presence of a strong base such as sodium hydride.
The intermediates of formula VIII above may be conveniently prepared by reacting a compound of formula III as defined above with an alkaline hydroxide, e.g. sodium hydroxide. The reaction is conveniently effected in an inert solvent such as 1,4-dioxane, ideally at the reflux temperature of the solvent. A compound of formula III in which G is para-sulphonyltoluene can be made by reacting a compound of formula VIII with 4-toluenesulphonylchloride.
Alternatively, the intermediates of formula VIII (or the tautomeric 5-ones, which are equally suitable for reaction with compounds of formula IX) may be prepared by reacting a compound of formula VI with a compound of formula XIV: 
wherein T1, T2, T3, T4, R1 and R2 are as defined above, under the conditions described above for the reaction of compounds of formula V with compounds of formula VI.
Where they are not commercially available, the starting materials of formula IV, VI, VIII, IX and XIV may be prepared by methods analogous to those described in the accompanying Examples, or by standard methods known from the art.
It will be understood that any compound of formula I initially obtained from the above process may, where appropriate, subsequently be elaborated into a further compound of formula I by techniques known from the art. For example, a compound of formula I in which one of T1, T2, T3 and T4 represents N can be converted to the corresponding compound in which T1, T2, T3 or T4 represents N+xe2x80x94Oxe2x88x92 by standard methods of oxidation, e.g. by means of m-chloroperoxybenzoic acid in an inert organic solvent at room temperature.
It will also be appreciated that where more than one isomer can be obtained from a reaction then the resulting mixture of isomers can be separated by conventional means.
Where the above-described process for the preparation of the compounds according to the invention gives rise to mixtures of stereoisomers, these isomers may be separated by conventional techniques such as preparative chromatography. The novel compounds may be prepared in racemic form, or individual enantiomers may be prepared either by enantiospecific synthesis or by resolution. The novel compounds may, for example, be resolved into their component enantiomers by standard techniques such as preparative HPLC, or the formation of diastereomeric pairs by salt formation with an optically active acid, such as (xe2x88x92)-di-p-toluoyl-d-tartaric acid and/or (+)-di-p-toluoyl-1-tartaric acid, followed by fractional crystallization and regeneration of the free base. The novel compounds may also be resolved by formation of diastereomeric esters or amides, followed by chromatographic separation and removal of the chiral auxiliary.
During any of the above synthetic sequences it may be necessary and/or desirable to protect sensitive or reactive groups on any of the molecules concerned. This may be achieved by means of conventional protecting groups, such as those described in Protective Groups in Organic Chemistry, ed. J. F. W. McOmie, Plenum Press, 1973; and T. W. Greene and P. G. M. Wuts, Protective Groups in Organtic Synthesis, John Wiley and Sons, 1991. The protecting groups may be removed at a convenient subsequent stage using methods known from the art.
The compounds in accordance with this invention potently inhibit the binding of [3H]-flumazenil to the benzodiazepine binding site of human GABAA receptors containing the xcex15 subunit stably expressed in Ltkxe2x88x92 cells.
Reagents
Phosphate buffered saline (PBS).
Assay buffer: 10 mM KH2PO4, 100 mM KCl, pH 7.4 at room temperature.
[3H]-Flumazenil (18 nM for xcex11xcex23xcex32 cells; 18 nM for xcex12xcex23xcex32 cells; 10 nM for xcex13xcex23xcex32 cells; 10 nM for xcex15xcex23xcex32 cells) in assay buffer.
Flunitrazepam 100 xcexcM in assay buffer.
Cells resuspended in assay buffer (1 tray to 10 ml).
Harvesting Cells
Supernatant is removed from cells. PBS (approximately 20 ml) is added. The cells are scraped and placed in a 50 ml centrifuge tube. The procedure is repeated with a further 10 ml of PBS to ensure that most of the cells are removed. The cells are pelleted by centrifuging for 20 min at 3000 rpm in a benchtop centrifuge, and then frozen if desired. The pellets are resuspended in 10 ml of buffer per tray (25 cmxc3x9725 cm) of cells.
Assay
Can be carried out in deep 96-well plates or in tubes. Each tube contains:
300 xcexcl of assay buffer.
50 xcexcl of [3H]-flumazenil (final concentration for xcex11xcex33xcex32: 1.8 nM; for xcex12xcex23xcex32: 1.8 nM; for xcex13xcex23xcex32: 1.0 nM; for xcex15xcex23xcex32: 1.0 nM).
50 xcexcl of buffer or solvent carrier (e.g. 10% DMSO) if compounds are dissolved in 10% DMSO (total); test compound or flunitrazepam (to determine non-specific binding), 10 M final concentration.
100 xcexcl of cells.
Assays are incubated for 1 hour at 40xc2x0 C., then filtered using either a Tomtec or Brandel cell harvester onto GFIB filters followed by 3xc3x973 ml washes with ice cold assay buffer. Filters are dried and counted by liquid scintillation counting. Expected values for total binding are 3000-4000 dpm for total counts and less than 200 dpm for non-specific binding if using liquid scintillation counting, or 1500-2000 dpm for total counts and less than 200 dpm for non-specific binding if counting with meltilex solid scintillant. Binding parameters are determined by nonlinear least squares regression analysis, from which the inhibition constant Ki can be calculated for each test compound.
The compounds of the accompanying Examples were tested in the, above assay, and all were found to possess a Ki value for displacement of [3H]Ro 15-1788 from the xcex15 subunit of the human GABAA receptor of 100 nM or less, most were at 50 nM or less, many were at 10 nM or less and some were at 1 nM or less.
The compounds of the present invention have been shown to enhance cognition in the rat water maze test (Morris, Learning and Motivation, 1981, 12 239ff). Further details of methodology for demonstrating that the present compounds enhance cognition can be found in WO-A-9625948.